Railway car hand brake mechanisms are well known in the art. They usually include a relatively large, rotatable hand wheel disposed in a vertical plane and mounted on a shaft which, through a gear train, can rotate a chain drum to wind up a chain that is secured at its end remote from the chain drum to the brake rigging of the railway car. As the hand wheel is rotated in one direction, the brakes are applied and rotation of the hand wheel shaft in the opposite direction is prevented by a holding pawl which engages a ratchet wheel on the hand wheel shaft.
One type of such hand brake mechanisms further includes a clutch mechanism for facilitating gradual release of the brake. When a hand wheel is rotated clockwise (as viewed from the front of the unit), such rotation is transmitted directly through a drive shaft, a pinion, a gear, and a winding drum to take up slack of a chain connected to the brake rigging. When resistance is offered by the chain to further rotation of the hand wheel, such resistance, acting back through the drum, the gear, and pinion, causes a nut to be advanced on a threaded portion of the drive shaft to move against a ratchet member which is clamped between respective friction surfaces on the nut and on the drive shaft, thus causing the drive shaft, ratchet wheel, and the nut to rotate as a unit. The pawl prevents rotation of the ratchet wheel in the opposite direction. The hand wheel torque is increased until a state of static equilibrium is reached, or at the point at which the brakes are fully applied, whereupon rotation of the hand wheel is terminated, and the clamped ratchet wheel, by means of the holding pawl, prevents the chain from unwinding.
The clutch mechanism also provides for quick release of the brakes by on the hand brakes equipped with a quick release handle. Manually rotating the quick release handle, generally in a clockwise direction as viewed from the front of the hand brake, effects disengagement of the normally engaged clutch and thereby allows free rotation of the pinion and gear to release the chain load while the nut and ratchet wheel are held stationary by the holding pawl. The brakes may also be released by disengaging the holding pawl from the detent wheel but this causes rapid rotation of the hand wheel and the gears of the gear train.
To avoid rapid rotation of the hand wheel, hand brake mechanisms have been devised which are known as “quick release” mechanisms. U.S. Pat. No. 4,368,648 issued to Housman et al. and entitled “Hand Brake for Railroad Car” teaches such hand brake having a quick release mechanism. The quick release mechanism includes a releasable connecting means between the hand wheel shaft and the gear train. When the connecting means is released, the gears of the gear train rotate rapidly, without constraint by the holding pawl and ratchet wheel, but the hand wheel remains stationary. The teachings of U.S. Pat. No. 4,368,648 are hereby incorporated in present application by reference thereto.
It has been found that when a hand brake is quick released using the quick release handle, the releasable connecting means between the hand wheel shaft and the gear train may not remain in released position due to the vibration or other unknown energy generated during train operation. As the result the railcar brakes may be applied unintentionally during railcar motion when the chain of the hand brake does not have enough slack to overcome partial release or the chain. It has been further found that some operators do not sufficiently hold the quick release handle in the released position to enable full release of the brakes.
It has also been found that many railroads object to the quick release handle being left in the released position and require for such handle to be returned due to gravity into the applied position while maintaining the railcar brakes in the released condition.
Therefore, there is a need for a release holding mechanism for use in a hand brake that prevents at least partial unintentional re-application of the railcar brakes and allows the return of the quick release handle into the initial applied position while maintaining the railcar brakes in the released condition.